Digital Commons Network^™

The Effect Of Particle Properties On The Flow Characteristics Of Electrophotographic Powders, Joseph Pedano

Theses and Dissertations

The effect of particle size on the flow characteristics and tribo-electrical charge of dry electrophotographic (toner) powders was investigated. Toner samples, consisting of the same base formulation, but differing in particle size were prepared and studied using commercially available processing and analytical equipment. The effect of post-blending fumed silica into the toner was also investigated as part of this work. The results indicate that toner particle size has a strong effect on toner flow characteristics. The flowability measurements that were most affected by the particle size were the cohesiveness and compressibility properties of the toner powders. The data showed that …

An Analysis Of Texture Resulting From Thermomechanical Processing Of Ti-6al-V, David J. Brock

Masters Theses

An investigation of texture and microstructure formation in Ti-6Al-4V after thermomechanical processing and heat treating was performed. X-ray diffraction was used to measure prismatic and pyramidal pole figures. These pole figures were used to calculate basal pole figures, which showed significant changes in texture from heavy rolling and near or above β-transus heat treatments. Primary texture components were found to be strengthened by near β-transus heat treatments. For heavily rolled material, above β-transus heat treatments were found to reverse the primary texture components order of dominants. Heavy rolling was found to reduce the RD component and strengthen the TD.

Reliability Analysis Of Frp Composite Columns, Jeremy Mcnutt

Masters Theses

Many companies are producing fiber reinforced polymeric structural shapes. At this time there has not been enough research performed to establish a load and resistance factor design approach. This thesis utilizes the work of Dr. Abdul-Hamid Zureick and his graduate students on concentrically loaded doubly symmetric fiber reinforced polymeric columns to develop the factors needed to implement a load and resistance factor design based design approach. This includes the selection of the target reliability index, the determination of the statistical properties of the material, the model error, and the development of the resistance factors used in design.

Feature Saliency In Artificial Neural Networks With Application To Modeling Workload, Kelly A. Greene

Theses and Dissertations

This dissertation research extends the current knowledge of feature saliency in artificial neural networks (ANN). Feature saliency measures allow for the user to rank order the features based upon the saliency, or relative importance, of the features. Selecting a parsimonious set of salient input features is crucial to the success of any ANN model. In this research, several methodologies were developed using the Signal to Noise Ratio (SNR) Feature Screening Method and its associated SNR Saliency Measure for selecting a parsimonious set of salient features to classify pilot workload in addition to air traffic controller workload. Candidate features were derived …

Mach Number Uniformity In A 16-Foot Supersonic Wind Tunnel At Arnold Engineering Development Center, David H. Smith

Masters Theses

Mach number uniformity in a 16-foot-square supersonic wind tunnel (Tunnel 16S) at the Arnold Engineering Development Center's Propulsion Wind Tunnel Facility was evaluated. Tunnel 16S is a continuous-flow, closed-circuit tunnel with a 101-foot-long, flexible-wall, Laval nozzle that can provide test-section Mach numbers from 1.50 to 4.75. It has been hypothesized that the observed Mach number nonuniformity is, at least partially, a result of two discontinuous regions in the nozzle contours. These discontinuous regions are a result of the nozzle-plate "lap joints", vertical seams in the nozzle walls. A 2-D, time-dependent, inviscid Euler code, NAP, was used to compute Mach number …

Handling Qualities Evaluation Of A Variable Stability Navion Airplane (N66ut) Using Frequency Domain Test Techniques, Randy Lee Bolding

Masters Theses

General aviation small aircraft handling quality certification has predominately been accomplished using traditional time-domain test techniques. This thesis investigates the handling quality characteristics of the variable stability Navion airplane, tail number N66UT, using frequency-domain test techniques. N66UT is configured with conventional flight controls at the copilot's station and a fly-by-wire set of flight controls at the pilot's station. Time delays between the fly-by-wire and conventional flight controls were determined to be minimal. Evaluation of handling qualities of the aircraft were compared to the fixed wing flying qualities speci fied in M IL-HDBK- 1 797. Analysis of flight test was conducted …

A Methodology For Acoustic Measurement And Separation Of Background Noise, Sekhar Radhakrishnan

Masters Theses

An attempt is made at developing experimental methods for the acoustic measurement and separation of background noise in a wind tunnel. To this end, an array beamforming technique known as delay-and- sum beamforming is identified and tested.

The theory underlying delay-and-sum beamforming is discussed. Two linear arrays, the seven microphone linear array and the four microphone minimum redundancy array, are designed. A driver is designed based on Helmholtz resonator theory to provide a source of monochromatic sound. Also, the concept of partial coherence as applicable to the separation of background noise from signal noise is investigated.

Array beamforming results show …

Effect Of Multiple Range Rings Vs. A Single Range Ring On Pilot Perception Of Vertical Separation On A Cockpit Display Of Traffic Information, Daniel B. Rizzardi

Master's Theses - Daytona Beach

The purpose of this study was to determine the effectiveness of both a two and four mile range ring versus a single three mile range ring on pilot's perception of future vertical separation as viewed on a cockpit display of traffic information. The subjects consisted of 30 volunteer pilots from Embry-Riddle Aeronautical University and the surrounding Daytona Beach, Florida area.

The simulation of a cockpit display of traffic information was generated using SuperCard® Version 1.6 software and a Macintosh IIx® personal computer. Eighty unique scenarios were monitored by the pilots in which they determined, as early as possible, what the …

Classification Of In-Flight Fatigue Cracks In Aircraft Structures Using Acoustic Emission And Neural Networks, Christopher Lee Rovik

Master's Theses - Daytona Beach

The research encompassed within this paper deals with the analysis and classification of fatigue cracks in aircraft structures. The particular structure that was examined was the vertical tail section of a Cessna T-303 Crusader aircraft. The analysis was performed using the nondestructive evaluation technique known as acoustic emission (AE), as well as the artificial intelligence of neural networks. Data were taken in a controlled laboratory environment as well as in a flying testbed aboard the aircraft.

The first part of the research involved the analysis of a typical aircraft structure in a controlled laboratory environment. This support structure was fabricated …

Adaptive Channel Equalization Techniques, Saied Razavilar

Masters Theses

Inter Symbol Interference (ISI) is a characteristic of band-limited communication channels that can severely degrade the digital communication system performance if not treated properly. Channel equalization techniques may be used to mitigate the effects of ISI in the system, thereby improving the system capacity and performance. In this thesis, the problem of Inter Symbol Interference caused by the nonlinear characteristics of band limited communication channels and adaptive equalization techniques to combat the effects of ISI are discussed. First, the analysis of ISI in a band limited communication channel using a concrete theoretical framework is presented. Next, various adaptive equalization techniques …

Fitness Landscape Analysis Of Discrete Constrained Optimization Problems, Sai Prasanna Ravichandran

Masters Theses

The exponentially large size of the solution space of typical optimization problems precludes the use of any deterministic approach to search for an optimal solution. A more efficient and efficacious approach is to use heuristic algorithms based on rules of thumb to guide the search process in the solution space. Associated with every solution in the space is a real number called fitness that signifies the quality of a solution. This space and the fitness values together form the fitness landscapes. Knowledge about the topology of these fitness landscapes is vital for any heuristic search operator to expedite the search …

Three-Dimensional Calculation Of Contaminant Transport In Groundwater At A Dover Afb Site, Tariq O. Hashim

Theses and Dissertations

Macroscale rate-limited sorption modeling was tested using a production transport code, the GMS/FEMWATER ground-water modeling package. The code (Version 1.1 of FEMWATER. dated 1 August 1995) was applied to a 3D conceptual model developed from a field site at Dover AFB, DE. A simulation was performed of a 200 hour contaminant injection pulse followed by clean water flushing. A moment analysis performed on the resulting breakthrough curve validated code self-consistency. Another injection pulse simulation showed that retardation temporally delays the breakthrough peak. Transport simulations of pulsed clean water pumping of the test cell with a prescribed initial contaminant distribution demonstrated …

Design Of The Computer Subsystem For The Afit Simulation Satellite (Simsat), Michael P. Hanke

Theses and Dissertations

This document details the systematic development of the computer subsystem for the AFIT Simulation Satellite (SIMSAT) from Concept Exploration to Implementation. This subsystem design effort was conducted as part of a larger four-phase team design effort to implement a fully functional, user-friendly test facility to meet current AFIT teaching and research requirements. Once SIMSAT system integration is complete, control laws will execute on the free-floating "satellite" to reduce communication systems overhead and its impact on control law execution, thereby allowing for more robust control system development and execution. Control law development, simulation, and interactive control of the system will occur …

How To Develop An Interactive Electronic Technical Manual: An Industry Perspective, Ali N. Karabulut, Hilmi Oz

Theses and Dissertations

Improvements in technology, especially in computer science, in the last two decades have made it possible, and preferable to develop digital technical manuals. A digital manual, which is called an Interactive Electronic Technical Manual (IETM), is a package of information required for the diagnosis and maintenance of a weapon systems, optimally arranged and formatted for interactive screen presentation to the end-user. Being the largest organization in the U.S., the Department of Defense has pioneered in the development of IETM concept as well as in the establishment of its standards. There have been many researches done about different IETM applications and …

Development Of An Operations Research Software Package For Army Divisions., Blane C. Wilson

Theses and Dissertations

There exists great potential for applying operations research techniques to solve specific problems in the areas of operations, installation support, and training at the Army division level. Because of the operational tempo of today's active-duty and reserve component units, command must focus on accomplishing the daily missions. Also, due their limited knowledge of the field, planners may not be aware of how operations research can be used to enhance planning and operations. Time, training funds, resources, safety, personnel, and equipment are all critical factors in this process. Operations research techniques could be used to improve division-level operations by saving time, …

Multi-Baseline Interferometric Sar For Iterative Height Estimation, Adam E. Robertson

Theses and Dissertations

Multiple SAR interferograms with judiciously selected height sensitivities can be iteratively combined to create a high accuracy digital elevation map. An initial height estimate is refined by iteratively using larger baselines to obtain a height estimation accuracy limited by the spatial decorrelation of the antenna baseline. Spatial filtering is used to reduce the propagation of errors for accurate height estimation. Images containing regions isolated by phase discontinuities, as often found in urban environments, can be resolved by this iterative multi-baseline technique. Computationally demanding and potentially unreliable phase unwrapping is not required to determine scene elevation using SAR inMultiple SAR interferograms …

Development Of A Discrete Ordinates Code System For Unstructured Meshes Of Tetrahedral Cells, With Serial And Parallel Implementations, Rodney L. Miller

Theses and Dissertations

A numerically stable, accurate, and robust form of the exponential characteristic (EC) method, used to solve the time-independent linearized Boltzmann Transport Equation, is derived using direct affine coordinate transformations on unstructured meshes of tetrahedra. This quadrature, as well as the linear characteristic (LC) spatial quadrature, is implemented in our transport code, called TETRAN. This code solves multi-group neutral particle transport problems with anisotropic scattering and was parallelized using High Performance Fortran and angular domain decomposition. A new, parallel algorithm for updating the scattering source is introduced. The EC source and inflow flux coefficients are efficiently evaluated using Broyden's rootsolver, started …

Case Study Comparisons Of Standard And Energy Efficient Polyphase Induction Motors Subjected To Unbalances Phase Voltages, Brian L. Bidwell

Masters Theses and Doctoral Dissertations

This study investigates the behaviors and economics of standard and energy efficient polyphase induction motors under unbalanced phase voltage conditions ofup to 5 percent. Motors sizes of 25, 50, 100,150,200, 250 and 300 hp are used in this investigation. Computer simulations are used to study the efficiencies, power losses and economics of motor behavior when unbalanced phase voltage system conditions exist. Previous polyphase induction motor studies simulated unbalanced phase voltage conditions by assuming a high impedance fault at the motor terminals. In this study, a method is used to simulate unbalanced phase voltage conditions by varying the phase voltage at …

Gas-Viscous Liquid Behavior And Its Implications For Pressure-Relief Design, Ahmad H. Alramadneh

Doctoral Dissertations

The two-phase flow system is a multifaceted engineering task with many industrial applications. The accurate prediction of the behavior of such systems is of special importance.

This study is directed toward improving and integrating what is known about the gas-viscous liquid flow behavior during vessel depressurization, specifically, visually characterizing the top venting of saturated-viscous fluids. The experimental results are needed to improve the design methodologies for pressure-relief systems.

Lab-scale vessel depressurization experiments with initially saturated fluids were performed. In particular, a problem arose when sodium tetraborate decahydrate solution (model fluid) saturated with carbon dioxide gas is vented from a 5.3-liter …

A Comparison Of Pseudo 3-Dimensional Collision Avoidance-Predictor Displays For Free Flight, Steve Kertesz Jr.

Master's Theses - Daytona Beach

This study was the second of two studies to evaluate the use of a pseudo three-dimensional display to present information about future possible conflicts. The purpose of this study was to evaluate variations of a cockpit screen display that transfers relevant data to the pilot in a manner which is easy to interpret and to facilitate the possible stressful situations that may be encountered due to the proposed free flight environment. In the first phase, three display concepts, using three different screen designs were compared. In this study, three different displays, all of which used using the space-time predictor concept …

Fatigue Life Prediction Of Edge-Welded Metal Bellows Using Neural Networks And Multiple Linear Regression, David L.W. Ballard

Master's Theses - Daytona Beach

Edge-welded metal bellows present an ongoing challenge: the prediction of an accurate cycle life. Current methods rely on physical leak detection to determine a bellow's cycle life to failure. It is known, however, that crack initiation begins many cycles before a leak path is present. Bellows manufacturers require a method for detection of fatigue cracks when they initiate but before they result in leak rates large enough to contaminate a process. Acoustic emission (AE) testing is one method which can meet this need and is a proven, reliable technique for detecting crack initiation and monitoring fatigue crack growth.

Four sets …

Modeling And Simulation Of High-Field, High-Temperature Sic Devices, Sanjay Pathak

Electrical & Computer Engineering Theses & Dissertations

With superior properties such as a large band gap, high thermal conductivity, and large electron drift velocity, SiC is expected to give a new dimension to high power, high temperature electronic devices used in power applications, microwave circuits, and for the space and automobile industries. SiC possesses an inherent advantage over its other large bandgap competitors in terms of inherited processing and device technology from Si. However, there is inadequate understanding of SiC device and its parameters. Simple extrapolations from Si are known to be inadequate. The aim of this dissertation, therefore. is to produce better understanding of SiC devices …

Skin-Stiffener Separation In Buckled Composite Plates And Shallow Shells, Mark Edward Robeson

Mechanical & Aerospace Engineering Theses & Dissertations

The development of an approximate analysis for predicting stresses in the skin-stiffener interface region of composite plates and shallow shells is presented. The analysis determines interlaminar normal stress and transverse shear stresses in the direction of the stiffener axial coordinate and the direction of the inplane coordinate perpendicular to the stiffener axis. The analysis accounts for skin-stiffener interfaces with nonzero thickness and for curvature in the skin and stiffener. The interlaminar normal stress and transverse shear stresses at the interface are applied to the lower face of the skin and the upper face of the stiffener flange as unknown functions, …

Value Of Increased Use Of Scheduled Maintenance On Aircraft Availability And Maintenance Cost Of The C-5, William T. Webb

Theses and Dissertations

The C-5 consistently performs below its established mission capable rate of 75 percent. The purpose of this study was to investigate whether or not mission capable rates and maintenance costs can be improved by increased use of scheduled maintenance. Nine C-5 components were studied. Availability and cost were compared when scheduled replacement occurred at ten, twenty, and thirty percent before their respective mean time between failure and actual failure times. Actual failure times were not available so they were generated using simulation. The trade-off of using preventive maintenance is the decreased cost of sending fewer maintenance repair teams and increased …

An Integer Program Decomposition Approach To Combat Planning, John C. Van Hove

Theses and Dissertations

Over the last two decades, our military forces have been working to incorporate the latest computer technology into the combat planning process. The earliest efforts use word processors, spreadsheets, and databases to organize planning data and to display high level summaries for commanders. Later efforts perform feasibility checks as missions are planned to insure that the necessary resources are available and that the assets requested are capable of meeting the assigned scheduling requirements. Some of the most recent computer planning tools have included the capability to automatically plan individual missions or groups of missions. These automated efforts have been heuristic …

Automatic Target Cueing Of Hyperspectral Image Data, Terry A. Wilson

Theses and Dissertations

Modern imaging sensors produce vast amounts data, overwhelming human analysts. One such sensor is the Airborne Visible and Infrared Imaging Spectrometer (AVIRIS) hyperspectral sensor. The AVIRIS sensor simultaneously collects data in 224 spectral bands that range from 0.4µm to 2.5µm in approximately 10nm increments, producing 224 images, each representing a single spectral band. Autonomous systems are required that can fuse "important" spectral bands and then classify regions of interest if all of this data is to be exploited. This dissertation presents a comprehensive solution that consists of a new physiologically motivated fusion algorithm and a novel Bayes optimal self-architecting classifier …

Feasibility Study On The Use Of The Internet For Traffic Of Unclassified Data, Alexandre L. Guerra, Luiz Gustavo F. P. Silva

Theses and Dissertations

This research compares two possible networking methods for connecting all Brazilian Air Force Materiel Command units responsible for support and operation of Brazilian Air Force's weapons systems. The network includes the use of dedicated X.25 links, and the use of a virtual Private Network using the Internet (TCP/IP) as the medium of transmission. The Brazilian Air Force Materiel Command, responsible to support operating units over a very large sparse territory, lacks an efficient media of computer communications, which makes it difficult to control the supply chain channels of materiel present in each unit, depots, and warehouses. We studied the network …

Monotonic And Fatigue Behavior Of 2-D Woven Ceramic Matrix Composite At Room And Elevated Temperatures (Blackglas/Nextel 312), Musa Al-Hussein

Theses and Dissertations

This study investigated the monotonic tension and compression and the tension-tension and tension-compression fatigue loading of Blackglas/Nextel 312 woven CMC at room temperature and at 760 degrees centigrade. Young's Modulus and strain variation were evaluated. S-N curves were obtained for room and elevated temperatures. The ultimate tensile stress was lower at the elevated temperature and it was higher in the compression test. Failure-strain was higher at the elevated temperature in both tension and compression tests. There was no significant change in Young's Modulus at the elevated temperature. Also, there was no difference in the number of cycles to failure at …

Effects Of Shiftwork On Air Force Aircraft Maintenance Personnel, Craig A. Campbell

Theses and Dissertations

This study examined the effects of converting a large aircraft maintenance squadron from 8-hour shifts to 12-hour shifts. The squadron studied converted its 24- hour maintenance work force from three 8-hour work shifts to two 12-hour work shifts incrementally, with one section converting to 12-hour shifts in January, 1996, and the remaining section converting in July, 1996. Both sections remained on 12-hour shifts until September, 1997, when both sections converted back to a three shift 8-hour operation. Health and well being, on- and off-duty accident rates, day shift vs. night shift accident rates, and the effects of stress and fatigue …

The Effects Of Three Media Presentation Systems On Maintenance Task Performance, John W. Chastain

Theses and Dissertations

Wearable computers and Portable Maintenance Aids (PMAs) may soon be the normal way of doing aircraft maintenance in the Air Force. Currently, the Air Force uses the paper form of Technical Orders (TO's) while doing aircraft maintenance. The purpose of this thesis was to compare the effects of three different media presentations of the information used during aircraft maintenance. The three different presentations compared are the current paper form, a Head Mounted Display (HMD), and an auditory mode. An experiment was conducted to determine if there was a significant difference between the systems (in terms of task completion times and …